Fire control and suppression sprinkler systems generally include a plurality of individual sprinkler heads which are usually ceiling mounted about the area to be protected. The sprinkler heads are normally maintained in a closed condition and include a thermally responsive sensing member to determine when a fire condition has occurred. Upon actuation of the thermally responsive member, the sprinkler head is opened, permitting pressurized water at each of the individual sprinkler heads to freely flow therethrough for extinguishing the fire. The individual sprinkler heads are spaced apart from each other, by distances determined by the type of protection they are intended to provide (e.g. light or ordinary hazard conditions) and the ratings of the individual sprinklers, as determined by industry accepted rating agencies such as Underwriters Laboratories, Inc., Factory Mutual Research Corp. and/or the National Fire Protection Association. It should be well appreciated that once the sprinkler heads have been thermally activated there should be minimal delay for the water flow through the sprinkler head at its maximum intended volume.
In order to minimize the delay between thermal actuation and proper dispensing of water by the sprinkler head, the piping that connects the sprinkler heads to the water source is, in many instances at all times filled with water. This is known as a wet system, with the water being immediately available at the sprinkler head upon its thermal actuation. However, there are many situations in which the sprinkler system is installed in an unheated area, such as warehouses. In those situations, if a wet system is used, and in particular since the water is not flowing within the piping system over long periods of time, there is a danger of the water within the pipes freezing. This will not only deleteriously affect the operation of the sprinkler system, should the sprinkler heads be thermally actuated while there may be ice blockage within the pipes, but such freezing, if extensive, can result in the bursting of the pipes, thereby destroying the sprinkler system. Accordingly, in those situations it is the conventional practice to have the piping devoid of any water during its non-activated condition. This is known as a dry fire protection system.
All fire protection sprinkler systems generally include a check valve for isolating the sprinkler system piping from the pressurized water source during the non-activated condition. The check valve, which is physically interposed between the system piping and the pressurized water source, includes a clapper, which when it is in its closed operative condition prevents the flow of pressurized water into the sprinkler system piping. The sprinkler piping in the dry fire protection system includes air or some other inert gas (e.g. nitrogen) under pressure. The pressurized air, which is present within the sprinkler system piping, is also presented to the check valve. Should one or more of the sprinkler heads be thermally activated to its open condition, the pressure of the air within the sprinkler system piping and check valve will then drop. The check valve must be appropriately responsive to this drop in pressure, normally in opposition to the system water pressure also present in the check valve, to move the clapper to its open condition. When this occurs, it is desirable to have a rapid expulsion of the pressurized air within the check valve and the sprinkler system piping, to permit the rapid flow of the pressurized water through the open check valve, into the sprinkler system piping, and through the individual sprinkler heads to rapidly extinguish the fire.
The check valves intended for dry type fire control sprinkler systems have typically controlled the clapper movement by the water and the air pressure applied to its opposite sides. Such fire check valves include an air seal which opposes the pressurized water seal. To appropriately apply the system air pressure over the surface of the clapper air seal, a priming water level is oftentimes maintained within the check valve. During normal conditions, when no sprinkler heads have been activated, the two seals will be at an equilibrium, thereby maintaining the clapper in its closed condition.
In order to increase the speed of check valve operation upon a drop off of the system air pressure, occasioned by the activation of one or more sprinkler heads, the system air pressure is normally applied to the clapper air seal over a substantially greater area than the water pressure is applied to the clapper water seal. This is known as a high differential type check valve. A problem of such valves is that should there be a reduction in the system water pressure after the clapper has opened, there is a tendency for the clapper to re-close, particularly since the pressure against the opposite (air) side of the clapper has thereby been increased due to the column of water that has flowed therethrough. Since the pressure applied against the air seal of the clapper will now be increased by the column of water extending upwards from the re-closed check valve, a greater water pressure would now be required to move the clapper to its open condition. Such disadvantageous re-closure is referred to as a water columning effect. This could result in failure of the check valve to subsequently open should one or more of the sprinkler heads be thermally activated.
In order to avoid the re-closure of the clapper, dry system check valves have generally been provided with a mechanical latch to maintain the clapper in its open condition once it has been activated. The inclusion of such a mechanical latch, while serving to prevent re-closure, however, disadvantageously requires the entire sprinkler system to be shut down and the interior of the high differential type actuator accessed to release the latch and re-close the clapper after the fire has been extinguished. Thus, check valves have typically required the main supply of water to be shut off, the water drained from the system, and then the high differential check valve opened to manually unlatch and reset the clapper. Recognizing the disadvantage of having to manually access the interior of the check valve, a mechanism is shown in U.S. Pat. Nos. 5,295,503 and 5,439,028, which include a reset linkage mechanism that is attached to the check valve, and is actuated by the rotation of an externally accessible handle. As can be well appreciated such a mechanism adds to the size, cost and complexity of the check valve.
Another way by which the response of a system check valve can be made faster upon activation is to incorporate an actuator-accelerator into the system. Actuator-accelerators for fire control and suppression sprinkler systems, including the low pressure actuator of the present invention, are pilot valves that are designed to actuate the check valve. Actuators for dry fire protection systems, including the low pressure actuator of the present invention, detect a decline in system gas pressure due to a triggering event such as the opening of a sprinkler head, and cause the valve to operate in order that water or another extinguishing liquid utilized in the system can flow into and fill the system as rapidly as possible so as to minimize the time it takes for the water to reach and be distributed to the multiple individual sprinkler heads of the system and be applied to extinguish a fire.
Traditionally, dry pipe valves used in sprinkler systems employ pressurized air in order to keep water from entering the sprinkler system. Although this pressurized air is given a mechanical advantage over the water pressure, typically of from about 5-8:1, typical air pressures in dry sprinkler systems are from 30 psi to 50 psi. Displacement of this volume of air from the piping of the sprinkler system will delay the operation of the sprinkler control valve, as well as slow the rate of water entry into the sprinkler system once the control valve is actuated.
For example, given a supply water pressure of 80 psi and a sprinkler control with an 8 to 1 water to air ratio, and given that a sprinkler head activates when the system air pressure is at 30 psi, the air pressure must decay from 30 to 10 psi before the valve will activate. Also, once the valve activates, the remaining 10 psi of air pressure must still be exhausted before the water can completely fill the sprinkler system.
In the case of using an actuator-accelerator, given a supply water pressure of 80 psi, if a head activates when the system air pressure is at 30 psi, the actuator-accelerator will activate on a rapid pressure drop of less than 5 psi. Although this will greatly reduce the time required for the valve to operate, the remaining 25 psi air pressure must still be exhausted before the sprinkler system becomes filled with water.
It is, therefore, advantageous to have as little air as possible in the system, in order to obtain the most rapid delivery of water to the sprinkler heads of a dry sprinkler system. One way of achieving this is to operate the system at a low system air pressure, of not more than about 20 psi, and preferably at about 10 psi, or even lower.